The present disclosure relates in general to the field of vehicle brake systems. In concrete terms, an electrohydraulic vehicle brake system with an electromechanical actuator for actuating the brake system is described.
Electromechanical actuators have already been used for some time in vehicle brake systems, for example to realise an electric parking brake function (EPB). In the case of electromechanical brake systems (EMB), they replace the conventional hydraulic cylinders on the wheel brakes.
Technical advancements have resulted in a continuous increase in the capacity of the electromechanical actuators. The use of such actuators in the implementation of modern vehicle-dynamics control systems has therefore also been taken into consideration. Such control systems include an antilock braking system (ABS), a traction control system (TCS) or an electronic stability program (ESP), also known as vehicle stability control (VSC).
WO 2006/111393 A discloses an electrohydraulic brake system with a high dynamic electromechanical actuator, which takes over the pressure modulation in the vehicle-dynamics control operation. The electromechanical actuator described in WO 2006/111393 A is provided to act directly on a master cylinder of the brake system. As a result of the high dynamics of the electromechanical actuator, the hydraulic components of the brake system disclosed in WO 2006/111393 A can be reduced to a single 2/2-way valve for each wheel brake. To realise individual pressure modulations for each wheel, the valves are then controlled individually or in groups in multiplex mode.
However, the minimisation to only one valve for each wheel brake also creates challenges such as an undesired pressure compensation when valves are open at the same time. A solution based on a high dynamic control behaviour for this is disclosed in WO 2010/091883 A.
WO 2010/091883 A discloses an electrohydraulic brake system with a master cylinder and a tandem piston received therein. The tandem piston can be actuated by means of an electromechanical actuator. The electromechanical actuator comprises an electric motor, which is arranged concentrically to the tandem piston, and a gear arrangement which converts a rotational movement of the electric motor into a translatory movement of the piston. The gear arrangement comprises a ball screw drive with a ball screw nut, which is coupled in torsion-resistant manner to a rotor of the electric motor, and a ball screw spindle acting on the tandem piston.
A further electrohydraulic brake system with an electromechanical actuator acting on a master cylinder piston is disclosed in WO 2012/152352 A. This system can operate in regenerative mode (generator operation).